factions error

[SEVERE] Could not load 'plugins\Factions.jar' in folder 'plugins':
java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
	at java.lang.reflect.Constructor.newInstance(Unknown Source)
	at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:136)
	at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:285)
	at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:200)
	at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:156)
	at org.bukkit.craftbukkit.CraftServer.<init>(CraftServer.java:132)
	at net.minecraft.server.ServerConfigurationManager.<init>(ServerConfigurationManager.java:52)
	at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:148)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:408)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:465)
Caused by: java.lang.NoClassDefFoundError: org/bukkit/potion/PotionEffectType
	at com.massivecraft.factions.listeners.FactionsEntityListener.<clinit>(FactionsEntityListener.java:231)
	at com.massivecraft.factions.P.<init>(P.java:66)
	... 13 more
Caused by: java.lang.ClassNotFoundException: org.bukkit.potion.PotionEffectType
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:41)
	at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:29)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	... 15 more